Circuit breakers are used in certain electrical systems for protecting an electrical circuit (hereinafter “protected circuit”) coupled to an electrical power supply. For example, circuit breakers may be conventional mechanical-type circuit breakers or electronic circuit breakers. Examples of electronic circuit breakers are ground fault circuit interrupters (GFCI) or arc fault circuit interrupters (AFCI). Both conventional mechanical and electronic circuit breakers (e.g., GFCIs and AFCIs) include tripping mechanisms that may provide persistent over-current protection as well as short circuit protection, and may provide for hand circuit breaker tripping as well. Although electronic circuit breakers (e.g., GFCI's and AFCI's) include an internal printed circuit board, which together with one or more onboard sensors may detect changes in an electrical condition within the protected circuit and trip a tripping mechanism, they also commonly include a tripping mechanism that has a bimetal element and armature adapted to passively trip the circuit breaker. During a current overload condition, the bimetal will bend and trip the armature.
Although constructions of such conventional circuit breaker tip mechanisms do allow for tripping at relatively low current thresholds, (at so-called low “instantaneous levels”), this has been at the expense of making certain components larger (e.g., magnets). Achieving instantaneous levels of about eight times their handle rating or less his has been an elusive goal for circuit breaker designers (e.g., 160 A for a 20 A breaker; 120 A for a 15 A breaker), especially in conventionally-sized components.
Accordingly, there is a long-felt and unmet need for a circuit breaker having low trip thresholds and small size.